class Solution {
public:
    void duplicateZeros(vector<int>& arr)
    {

        int cur = 0;
        int dest = -1;
        int n = arr.size();

        while (cur < n)
        {
            if (arr[cur] != 0)
            {
                dest++;
            }
            else
            {
                dest += 2;
            }

            if (dest >= n - 1)
            {
                break;
            }
            cur++;
        }

        if (dest > n - 1)
        {
            arr[n - 1] = 0;
            dest -= 2;
            cur--;
        }

        while (cur >= 0)
        {
            if (arr[cur] != 0)
            {
                arr[dest--] = arr[cur--];
            }
            else
            {
                arr[dest--] = 0;
                arr[dest--] = 0;
                cur--;
            }
        }
    }
};